Fri, Jan 22, 2016, 1:00 pm to 2:15 pm
Searching for new exotic quantum phenomena is one of the fundamental goals and driving forces of condensed matter physics. Recent advances in the atomic-scale controlled synthesis techniques enable us to design and fabricate heterostructures for generating new quantum states, such as the emergent high-temperature superconductivity (HTSC) in single-layer FeSe films on SrTiO3. Elucidation of the mechanism underlying the HTSC has been hindered by the extremely narrow tunability of SrTiO3 interfacial parameters. In this talk, I will present our recent work on a new heterostructure with HTSC, single-layer FeSe film on anatase TiO2(001), which is prepared by molecular beam epitaxy (MBE) technique. In situ scanning tunneling microscopy/spectroscopy (STM/S) study reveals that it exhibits a large superconducting gap ranging from 17 meV to 21 meV, as well as a nearly square vortex lattice under magnetic field, which indicates that the superconducting gap is strongly four-fold anisotropic in momentum space. The comparison study between TiO2 and SrTiO3 clarifies the crucial roles of the substrates, primarily via interfacial electron-phonon coupling and charge transfer, in realizing HTSC. By further visualizing oxygen vacancies at the interface and tuning their density, we find they have very limited effect on the superconducting gap magnitude, excluding the interfacial oxygen vacancies as the primary source of charge transfer. Our findings could place severe constraints on any microscopic proposal for HTSC in single-layer FeSe-related heterostructures.